System and method to reduce transmit wander in a digital subscriber line

Abstract

A system and method for reducing transmit carrier wander in a DSL communication system are disclosed. A network timing reference unit provides an automatic embedded solution for synchronizing DSL frames to an external communication system reference clock. The network timing reference unit applies or removes bits to adjust the length of a DSL frame in response to a sliding window state table. A sliding window is selected in response to the relative position of the DSL frame to a system clock reference point over a number of DSL frames. A network timing reference unit in accordance with the present invention may comprise a counter, a network timing latch, a synchronization word detector, a DSL frame latch, a lead/lag comparator, a sliding window buffer, a sliding window state table, a DSL frame state recorder, and a sensitivity buffer. The present invention provides a method for reducing transmit carrier wander in a DSL transceiver. In its broadest terms, the method can be described as: receiving a network clock and a DSL data stream comprising a plurality of frames; identifying a reference point on the network clock signal; identifying a DSL frame reference point; recording the relative position of the DSL frame reference point to the network clock reference point; performing a bit-manipulation responsive to the relative reference positions and a current window position; and adjusting the current window position in response to a consistent relative reference position between the network clock and DSL frame reference points.